The present invention concerns a rotor blade for a wind energy plant, with at least one recess, arranged in the region of the rotor blade base and extending essentially transversely to the longitudinal access of the rotor blade, for accommodating a cross bolt, which can be coupled to a tensioning element for the connection of the rotor blade to a rotor hub of a wind energy plant.
The invention further concerns a rotor for a wind energy plant with a rotor hub and at least one rotor blade fastened to the rotor hub, as well as a wind energy plant with such a rotor.
A rotor blade as well as such a rotor for a wind energy plant, of the type named in the introduction, are known. They find application, for example, in a wind energy plant with the designation AEOLUS II, which was developed as an experimental plant by Messerschmidt-Bxc3x6lkow-Blonm (MBB) (xe2x80x9cWindkraftanlagenxe2x80x9d, Erich Hau, 2nd ed., Springer-Verlag, Berlin, Heidelberg, New York, ISBN 3-540-5743-1, p. 203).
With wind energy plants, the fastening of the rotor blades, which are subjected to considerable forces, to the shaft of the wind energy plant, which is coupled to the generator, is a general problem, since due to the forces acting upon the rotor the components used are exposed to extreme stresses. The structural form of the so-called rotor blade connection is thus of great significance.
With one known wind energy plant, the rotor blade, consisting of a compound material, is connected in the region of the so-called rotor blade base, i.e. in the rotor blade""s end region that is to be coupled to the rotor hub, to a metallic flange that consists of an inner and outer ring flange; in this, the rotor blade base is set between the inner and the outer ring flange and is fastened by means of an adhesive and a threaded connection. For the producing of the threaded connection, a bolt is inserted through a passage bore, which passes completely through the rotor blade, into the rotor blade and screwed. The flange is screwed to the rotor hub at its end opposite to the rotor blade base. This construction of the rotor blade connection is relatively complicated and heavy structurally, since the metallic flange has a high weight. Especially disadvantageous is the fact that the rotor blade is significantly weakened in the region of the rotor blade base by the passage bore for receiving the bolt.
An additional, known wind energy plant displays as the rotor blade connection a steel flange joint, in which the rotor blade base is clamped between an inner and an outer flange and the two flanges are screwed together. The joining of the two flanges with the rotor hub takes place by means of a spaced-apart flange ring, with the aid of high-strength expansion screws. In this construction the metallic flanges contribute very often up to a third to the total weight of the rotor blade. Furthermore, the force progression is unfavorable, due to a radial offset between the rotor blade base and the spaced-apart flange, since this leads to an undesired lever effect.
In the case of the above mentioned experimental AEOLUS II, a so-called cross-bolt connection is used, in which the so-called cross bolts are arranged in passage bores in the region of the rotor blade base (i.e. the hub-side end region of the rotor blade), which passage bores are formed in the rotor blade and pass completely through the latter. The cross bolts arranged inside the passage bores are laminated into the rotor blade and serve as anchoring elements inside the rotor blade. The cross bolts are in each case connected to a tensioning element, formed as a bolt-shaped tension rod, that is screwed together with the rotor hub. By means of the tensioning element, which is subjected to tension, the rotor blade is pressed against the hub and thus held. In this construction it is likewise especially disadvantageous that the rotor blade is greatly weakened in the region of the rotor blade base by the passage bores for receiving the cross bolts. Furthermore, the force progression in the region of the flange-like rotor hub is unfavorable.
The task of the present invention consists in specifying a rotor, a rotor blade, and a wind energy plant, in which the disadvantages of the prior art are to a large extent avoided, and which have an easily producible and secure connection between the rotor blade and the rotor hub, which connection is able to withstand extreme stresses.
According to the invention, this task is accomplished in a rotor blade as well as a rotor of the type named in the introduction by the fact that the recess passes only partially through the rotor blade.
By means of the design, in accordance with the invention, of a recess that passes not completely, but rather only partially, through the rotor blade, the rotor blade is weakened in the region of the rotor blade base to a substantially lesser degree than is the case with the prior art, in which provision is made for a passage bore that passes completely through the rotor blade for receiving the cross bolt. Achieved according to the invention is the fact that the rotor blade, by virtue of the reduced material weakening, can withstand greater stresses with comparable structural size. A rotor blade is thus more securely fastened to a hub of a wind energy plant, and the structural size of the rotor blade connection can be kept relatively small, so that it can be built so as to be comparatively light. The rotor blade connection according to the invention withstands in a lasting manner the extreme stresses to which the rotor blade and the rotor hub are subjected in the region of the rotor blade base.
With the use in particular of fiber-reinforced epoxy-resin compound material as a lighter and at the same time more robust material for rotor blades, a durable anchoring of the cross bolts in the rotor blade base can be realized. In this case there results a favorable introduction of force from a cross bolt to the epoxy-resin compound material of the rotor blade.
An especially preferred implementation of the rotor blade according to the invention and of the rotor blade is characterized by the fact that the recess is formed as a pocket hole. In this way, the recess can be formed in the rotor blade in a particular simple manner from the outside. A further advantage results from the fact that the cross bolts, which in the assembled state are arranged inside the pocket holes accessible from the outside, can, if need be, be replaced without any damage to the rotor blade being necessary.
Provision can advantageously be made in the rotor blade for several spaced-apart pocket holes for receiving several cross bolts, since thereby the strength of the rotor blade connection can be substantially increased, which is necessary in particular in the case of very large wind energy plants. The pocket holes can be spaced in such a manner that the material is only insignificantly weakened by the pocket holes.
Especially preferable is an implementation of the invention in which the rotor blade has an enlarged cross section in the region of the rotor blade base and the pocket holes or holes is/are arranged in the region of the enlarged cross section. Also, through this measure the load capacity of the connection between rotor blade and rotor hub can be significantly increased, since the rotor blade, due to the enlargement of the cross section in the region of the rotor base, is subjected to substantially smaller stresses and can therefore be impinged upon by greater forces. By means of the arrangement, according to the invention, of the pocket holes in the region of the enlarged cross section, a favorable introduction of force from the cross bolts to the material of the rotor blade is possible, while a substantially lesser surface pressure occurs at the contact surface between the cross bolts and the inner surface of the recess.
According to an especially preferred implementation form of the invention, the cross section of the rotor blade is enlarged on both sides in the direction of a hub-side end section of the rotor blade. In this way a symmetrical introduction of force from the cross bolts into the robust rotor blade is realized. According to a further development of this implementation example, the rotor blade displays two opposite-lying thickening sections, in each case formed as one piece with the rotor blade, and the pocket holes are arranged at least partially in the region of a thickening section. The thickening sections, which contribute to the cross section enlargement, can be formed in a simple manner through the laminating on of several layers of fiber laminate material and epoxy resin.
Especially preferred, furthermore, is an implementation form in which the rotor blade displays in the region of the rotor blade base an essentially pipe-shaped end section, in which several pocket holes are formed on the inside and outside. A pipe-shaped end section can be attached to the rotor hub in an especially uniform and simple manner and is of particular advantage in the case of very large wind energy plants, in which extreme forces appear, the rotor blades of which transition from the pipe-shaped end section for attachment into a wing-profile section.
A further development is characterized through several bores, each joined with a pocket hole and extending essentially in the direction of the longitudinal axis of the rotor blade, for receiving in each case a tensioning element that can be connected to a cross bolt. In this manner the tensioning elements are advantageously arranged partially inside the rotor blade in the bores and can at the same time engage a bore that is arranged centrally in the cross bolts and provided with a tread, so that the cross bolts are impinged upon by the tensile force in a symmetrical manner and are arranged inside the rotor blades essentially free of moments.
A favorable introduction of force and a high strength result when the pocket hole or holes is/are essentially cylindrical and display a depth that is approximately equal to a third of the cross section of the rotor blade in the region of the rotor blade base.
A great lightness of material combined with a high degree of strength results from an implementation form in which the rotor blade consists mainly of a glass-fiber-reinforced epoxy-resin compound material.
The previously explained advantages of a rotor blade according to the invention result in a similar way from a rotor for a wind energy plant of the type mentioned in the introduction, which plant is equipped with a rotor blade according to the invention. In order to avoid repetition, therefore, with respect to these advantageous effects reference is made to the foregoing exposition.
A preferred further development of the rotor according to the invention is distinguished by the fact that the rotor hub displays a rotary, in cross section essentially T-shaped flange section for the connecting of the rotor blade and that the rotor blade is screwed to the flange section by means of several tensioning elements, which are connected in each case to a cross bolt anchored on the rotor blade. Through the advantageous symmetrical T-shaped flange section a symmetrical force introduction from a rotor blade to the hub can be realized, since formed in the two open sections of the T-shaped flange section, lying essentially in one plane, are the passage bores through which the tensioning elements project. Advantageously, the several tensioning elements are arranged parallel to each other in pairs and essentially in two rows that are concentric with each other. In this, the tensioning elements lying opposite each other in pairs can lie directly opposite or staggered with respect to the tensioning elements of the other row.
The advantages according to the invention are also realized by a wind energy plant that is equipped with a rotor and/or a rotor blade of the above-described type; with respect to the advantages according to the invention that are attainable thereby, reference is made to the foregoing explanations in connection with a rotor blade and rotor according to the invention.